If you are a foreign national living in the U.S. as a permanent resident, it is crucial that you learn English in order to fully assimilate into American society. Learning English does not imply giving up your native language, nor does it mean that it is better than your native language. However, you must speak the local language in order to obtain the most from living in the United States. English is crucial for getting a good job, for attending school and university, for enjoying local entertainment, for conversing with service people, and for dealing with small, everyday matters such as a telephone call or trip to the bank.
Speaking English is a travel aide if you plan to visit a foreign country. Many airports use both the local language and English to help foreigners navigate through luggage check, security, customs and transfers. When traveling to a foreign country, the best language to know is the one that is spoken locally, but if you are traveling to multiple countries located on every corner of the globe, learning every language is impossible. English, though it may not always work, is the one language that is most likely to be spoken as a second language by locals. If you are lost, no matter what your native language is, if you can ask directions in English, someone will eventually be able to answer you.
English is the modern lingua franca of business, that is, when there is no common language shared, the transaction is completed in English. A Brazilian businessman negotiating with a partner in Turkey most likely speaks neither Portuguese nor Turkish and instead communicates with English. English is a requirement for any form of international business; whether you are in Europe, South America, Asia or the Middle East, English is the connecting language. International companies rarely hire employees who do not speak English, as negotiation is usually required with companies based in many different countries.
English language fluency is a significant asset to any résumé, whether for employment or entrance into a college or education program. Persons intending to study at a university in the U.S. or UK must be able to speak English in order to pass admissions. The vast majority of companies in the U.S. only hire employees who speak English. Having English proficiency on a résumé is a critical tool for landing jobs in any foreign country, as well. A French multinational company located in Brazil would hire an applicant who can speak English over one who cannot, without hesitation.